Crystal structure of (E)-2-{[(4-anilinophenyl)imino]methyl}-4-nitrophenol

The title compound, C19H15N3O3, features an intramolecular O—H⋯N hydrogen bond and an E conformation for the Schiff base unit.


Chemical context
Schiff bases derived from 2-hydroxy-5-nitrobenzaldehyde are widely used either as materials or as intermediates in explosives, dyestuffs, pesticides and organic synthesis (Yan et al., 2006). Intramolecular hydrogen-atom transfer (tautomerism) from the o-hydroxy group to the imine-N atom is of prime importance with respect to the solvato-, thermo-and photochromic properties exhibited by o-hydroxy Schiff bases (Filarowski, 2005;Hadjoudis et al., 2004). Such protonexchanging materials can be utilized for the design of various molecular electronic devices (Alarcó n et al., 1999). As part of our ongoing studies of Schiff bases and their complexes (Faizi et al., 2016), we now report the synthesis (from 2-hydroxy-5nitrobenzaldehyde and N-phenyl-p-phenylenediamine) and crystal structure of the title compound, (I).

Structural commentary
The molecular structure of the title compound, (I), is illustrated in Fig. 1. There is an intramolecular O-HÁ Á ÁN hydrogen bond (Table 1), which is a common feature in related imine-phenol compounds. The imine group displays a C6-C7-N2-C8 torsion angle of 177.1 (3) and the nitro phenol ring (C1-C6) is inclined to the central benzene ring ISSN 2056-9890 (C8-C13) by 6.24 (4) . The overall twisted conformation of the molecule is largely determined by the orientation of the terminal aminophenyl ring (C14-C19) with respect to the central benzene ring (C8-C13); the dihedral angle between them is 47.18 (4) . The two outer aromatic rings (C1-C6 and C14-C19) are inclined to one another by 42.08 (4) . The C1-O1 distance [1.351 (4) Å ] is close to normal values reported for single C-O bonds in phenols and salicylideneamines (Ozeryanskii et al., 2006). The N2-C7 bond is short at 1.287 (4) Å , strongly indicating the existence of a conjugated C=N bond, while the long C6-C7 bond [1.445 (4) Å ] implies a single bond. All these data support the existence of the phenol-imine tautomer for (I) in its crystalline state. These features are similar to those observed in related 4-dimethylamino-N-salicylideneanilines (Filipenko et al., 1983;Aldoshin et al., 1984;Wozniak et al., 1995;Pizzala et al., 2000).

Figure 2
A view down [001] of the N-HÁ Á ÁO and C-HÁ Á ÁO interactions (shown as dashed lines) in the crystal of the title compound.

Figure 1
The molecular structure of the title compound, with displacement ellipsoids drawn at the 40% probability level. The intramolecular O-HÁ Á ÁN hydrogen bond is shown as a dashed line.
then added and the mixture was refluxed for 2 h. The resulting reddish yellow precipitate was recovered by filtration, washed several times with small portions of EtOH and then with diethyl ether to give 150 mg (83%) of the title compound. Colourless blocks of (I) were obtained within three days by slow evaporation of a solution in methanol.

(E)-2-{[(4-Anilinophenyl)imino]methyl}-4-nitrophenol
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.